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BAHAN KAJIAN MK. DASAR ILMU TANAH SIFAT FISIKA TANAH Dihimpun oleh Soemarno Jurusan Tanah FP UB Februari 2012.

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Presentasi berjudul: "BAHAN KAJIAN MK. DASAR ILMU TANAH SIFAT FISIKA TANAH Dihimpun oleh Soemarno Jurusan Tanah FP UB Februari 2012."— Transcript presentasi:

1 BAHAN KAJIAN MK. DASAR ILMU TANAH SIFAT FISIKA TANAH Dihimpun oleh Soemarno Jurusan Tanah FP UB Februari 2012

2 TEKSTUR TANAH Efek Ukuran partikel tanah

3 … Diunduh 15/2/2012 Tipe-Tipe Struktur Tanah Common to Ohio soils just below Ap (> 8”) Plow layer Sand Deeper in profile (>3-4’) Granular Platy Prismatic Columnar Blocky Single Grain Massive

4 TEKSTUR TANAH Luas permukaan internal Pori tanah Relative proportion of the various size separates in a soil. Important because it affects and is related to several soil properties such as soil structure, aeration, water holding capacity, nutrient storage, water movement, and bearing strength.

5 Fraksi Tanah = Soil Separates Mineral soil is considered as a porous mixture of inorganic particles, decaying organic matter, water and air. Particle size and particle size distribution of these inorganic particles have an important bearing on the physical properties of soil. TEKSTUR TANAH

6 Soil separates do not act as individuals, but as partners, or aggregates. Aggregates are the clumps of soil separates. When aggregates are bound together into large masses they are called peds It is difficult to alter the soil texture on the field level.

7 TEKSTUR TANAH Mineral fraction of soil is divided into are called soil separates. three major size groups. These groups Sand mm to 2 mm in diameter Silt mm to 0.05 mm in diameter Clay - <0.002 mm Gravel - 2 mm to 2 cm Stones - >2 cm Particles of <0.001 mm are designated as colloids - clay, a colloid is unique because of its large surface area.

8 Klasifikasi tekstur tanah Penentuan tekstur tanah TEKSTUR TANAH

9 Karakteristik kelas tekstur Modifiksi tekstur tanah TEKSTUR TANAH

10 “Big”  smaller  really small Sand  silt  clay Perbandingan ukuran partikel tanah

11 Surface area per unit volume –1 g sand ~ 0.1 m 2 –1 g silt ~ 1 m 2 –1 g clay ~ m 2 lowest highest Large surface area means more charge so greater ability to hold water and nutrients Coarse textured soils have larger pores, fine textured soils have greater total pore space Gee whiz fact: Fine clay has ~10,000 times as much surface area as the same wt. med. grain sand h Surface area h weathering TEKSTUR TANAH

12 Surface area, pore volume, nutrient supply capacity, plasticity and cohesion, swelling Particle Size Clay SiltSand

13 Clay SiltSand Pore size, infiltration rate, drainage rate, aeration

14 Siklus Hidrologi dan Tanah Color Structure Bulk Density Texture pH Temperature Moisture Horizon Depths Sifat tanah yang menjadi bagian dari siklus hidrologi.

15 PENGARUH TEKSTUR PasirDebuLiat Water-holding capacity Aeration Drainage Nutrient retention LowMediumHigh GoodPoor Medium SlowVery slowFast HighLowMedium

16 DENSITAS DAN PERMEABILITAS TANAH Kerapatan partikel = Particle density

17 Bobot Isi Tanah Porositas Tanah DENSITAS DAN PERMEABILITAS TANAH Permeabilitas tanah ditetapkan dalam keadaan jenuh pada contoh tanah yang tidak terganggu yang dirumuskan : K = (QL) / t.h.A. Dimana : K = Permeabilitas ( cm/jam ) Q = Banyaknya air setiap pengukuran ( cm3 ) L = Tebal contoh tanah ( cm ); H = Tinggi permukaan air dari permukaan tanah ( cm2 ) A = Luas permukaan contoh tanah ( cm2 ) t = Waktu ( jam )

18 Permeability DENSITAS DAN PERMEABILITAS TANAH

19 BOBOT ISI – BULK DENSITY Calculate soil bulk density and % pore space Discuss factors influencing the above soil properties Identify the difference between texture and structure Bobot isi tanah merupakan kerapatan tanah per satuan volume yang dinyatakan dalam dua batasan berikut ini: (1)Kerapatan partikel (bobot partikel = BP) adalah bobot massa partikel padat per satuan volume tanah, biasanya tanah mempunyai kerapatan partikel 2,6 gram cm-3, dan (2) Kerapatan massa (bobot isi = BI) adalah bobot massa tanah kondisi lapangan yang dikering- ovenkan per satuan volume. bobot-isi.htmlhttp://dasar2ilmutanah.blogspot.com/2009/04/sifat-fisika-tanah-bagian-3- bobot-isi.html..... Diunduh 16/2/2012

20 Density Porosity – particle density: mass per unit volume (not pore space) bulk density: mass per unit volume (including pore space) the volume percentage (%) of the total bulk soil NOT occupied by solids ~ 2.65 Mg/m 3 (D p of quartz mineral, dominant mineral in most soils) ranges 0.1 – 2.65 Mg/m 3 BOBOT ISI – BULK DENSITY

21 O.M. decreases bulk density Compaction increases bulk density Increased bulk density lowers water infiltration and restricts root growth Mass of dry soil per unit bulk volume, INCLUDING pore space Bulk density is relatively high in coarse-textured soils because total pore volume is low BOBOT ISI – BULK DENSITY

22 Histosols ( Mg/m 3 ) Cultivated clay and silt loams ( Mg/m 3 ) Cultivated sandy loams and sands ( Mg/m 3 ) Concrete (ca. 2.4 Mg/m 3 ) Quartz mineral (2.65 Mg/m 3 ) LOW HIGH BOBOT ISI – BULK DENSITY

23 OM: ~0.5 Mg/m 3 “normal” soils: D b ~ Mg/m 3 –Clayey soils lower than sandy soils Upper limit: ~2.65 Mg/m 3 BOBOT ISI – BULK DENSITY Kerapatan massa lapisan yang bertekstur halus biasanya antara 1,0-1,3 g/cm3. Jika struktur tanah kasar maka kerapatan massa 1,3-1,8 g/cm3. Semakin padat suatu tanah makin tinggi kerapatan massa atau bulk densitynya sehingga makin sulit meneruskan air atau ditembus oleh akar tanaman. %20II.pdfhttp://repository.usu.ac.id/bitstream/ /16232/4/Chapter %20II.pdf Diunduh 15/2/2012

24 Effect varies with soil texture! BOBOT ISI – BULK DENSITY

25 Soil bulk density on skid trails: does tillage help??

26 TextureYrs cropped Increase in D b due to texture and cultivation Loam58 Silt loam40 Clay70 In general, the finer the texture, the more it compacts if aggregates are destroyed Coarse Fine BOBOT ISI – BULK DENSITY

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28 STRUKTUR TANAH Tanah tidak berstruktur

29 Tipe-tipe struktur tanah Pembentuka struktur tanah STRUKTUR TANAH Agregasi tanah merupakan proses-proses dimana partikel tanah utama (pasir, debu, liat) terikat bersama-sama oleh gaya alami dan bahan-bahan yang dihasilkan oleh eksudat akar dan aktifitas mikrobia. Agregat Suatu unit struktur tanah yang terbentuk oleh proses alami yang berlawanan dengan proses buatan, dan biasanya berdiameter <10 mm. Agregat yang stabil air adalah suatu agregat yang stabil dengan gaya-gaya yang diakibatkan oleh air seperti titik hujan, atau agitasi dalam analisa saringan basah.

30 Structure – Aggregate stability – spatial arrangement of primary soil particles how easily or not do the peds fall apart? Low bulk density Lots of macropores Stable aggregates Goal of good soil mgmt. STRUKTUR TANAH

31 The arrangement of primary soil particles into groupings called aggregates or peds Binding agents provided by plant roots (exudates), organic matter (OM), and clays Most important contributor to good structure is OM STRUKTUR TANAH

32 Perbedaan antara Tekstur dan struktur Texture = proportions of different particle sizes (% sand, silt, clay) Structure = spatial arrangement of those particles STRUKTUR TANAH

33 Agregasi tanah dihasilkan dari penyusunan partikel, flokulasi, dan sementasi yang diperantarai oleh bahan organik tanah, biota tanah, jembatan ionik, liat, dan karbonat. Struktur tanah yang baik memiliki kemantapan agregat yang diperlukan untuk meningkatkan ketersediaan hara bagi tanaman, produktivitas tanaman, porositas, dan menurunkan tingkat erosi. Konsep dasar dari agregasi adalah pembentukan partikel sekunder melalui penggabungan partikel mineral dengan bahan organik dan anorganik. Dinamika agregasi sangat kompleks dan dipengaruhi oleh interaksi beberapa faktor seperti lingkungan, pengelolaan tanah, tanaman, komposisi mineral, tekstur, konsentrasi karbon organik tanah, proses pedogenesis, aktivitas mikroorganisme tanah, ion-ion yang dapat dipertukarkan, cadangan nutrisi di dalam tanah, dan kelembaban Particles bind because organic compounds and some minerals are “sticky” –Biological sources: polysaccharides, proteins, bacterial “glues” –Mineralogical sources : oxides, carbonates, silicates (clay particles) STRUKTUR TANAH

34 KARAKTERISASI STRUKTUR Type: –Four (4) principal shapes Granular (A), platy (E), blocky (B), prismatic (B) Size –fine, medium, coarse Grade: –Strong, moderate, or weak In general, –if lots of clay  STRONG structure, bigger blocks –If lots of OM  granular structure Shape of the aggregates distinctness (how obvious)

35 TIPE STRUKTUR: Spheroidal

36 Structure type: Platey

37 Structure type: Blocky

38 Structure type: Prism-like Sodium induced – disperses clays

39 C B E A Granular Platy Blocky Massive

40 TELADAN LABEL STRUKTUR TANAH GRADE SIZE TYPE Moderate coarse subangular blocky Weak medium platy Strong very coarse prismatic Moderate very fine granular

41 AGREGAT ADALAH UNIT STRUKTUR Amount of OM Type and amount of clay Amount of stabilizing/flocculating minerals (calcium carbonate, gypsum, etc.) The same things that lead to strong structure make stable aggregates!

42 AGREGAT Aggregates contain many small pores; area between aggregates large pores Total ruang pori dapat dihitung dengan menggunakan data bobot jenis partikel – partikel dan bobot isi tanah sebagai berikut: TRP = 1 - BD/PD. 100% Dimana: TRP = Total Ruang Pori ‘ BD = Bulk Density (g/cm3) ; PD = Partikel Density

43 MENGAPA AGREGAT TANAH SANGAT PENTING? Increase porosity Increase water infiltration, drainage, decrease runoff Increase water holding capacity Ruang pori tanah ialah bagian yang diduduki udara dan air. Jumlah ruang pori sebagian ditentukan oleh susunan butir-butir padat, apabila letak keduannya cenderung erat, seperti pada pasir atau subsoil yang padat, total porositasnya rendah. Sedangkan agregat bergumpal seperti yang kerap kali terjadi pada tanah-tanah yang bertekstur sedang yang besar kandungan bahan organiknya, ruang pori persatuan volume akan tinggi.

44 KONDISI YANG MEMPERBAIKI STABILITAS AGREGAT 1.Low disturbance 2.High root abundance 3.High fungal biomass 4.High OM 5.High clay content Pembentukan agregat terjadi melalui beberapa cara dan dikelompokkan dalam tingkat ukuran yaitu makroagregat (> 250 μm) dan mikroagregat (< 250 μm). Teori agregasi yang dikemukakan Tisdall (1996) adalah mikroagregat (< 250 μm) dibentuk oleh molekul organik (MO) yang menempel pada liat (L) dan kation polivalen (P) membentuk partikel (L-P- MO), yang saling berikatan dengan partikel (L-P- MO) lainnya membentuk makroagregat [(L-P- MO)x]y.

45 EFEK BOT TERHADAP STABILITAS AGREGAT Mekanisme agregasi melalui proses flokulasi dan fragmentasi. Flokulasi terjadi jika partikel tanah yang pada awalnya dalam keadaan terdispersi, kemudian bergabung membentuk agregat. Sedangkan fragmentasi terjadi jika tanah dalam keadaan masif, kemudian terpecah-pecah membentuk agregat yang lebih kecil. Semakin mantap suatu agregat tanah, semakin rendah kepekaannya terhadap erosi (erodibilitas tanah).

46 Efek akar dan pengolahan tanah terhadap stabilitas agregat Kemantapan agregat tanah dipengaruhi oleh : (i)jumlah dan jenis bahan organik di dalam tanah, khususnya lem dan musilage, (ii) keberadaan bakteri dan fungi serta akar tanaman berukuran mikro, (iii) pembasahan dan pengeringan, (iv) freezing dan thawing, (v) situs pertukaran kation alami, dan (vi) aktivitas biota tanah khususnya cacing tanah.

47 Cara memperbaiki struktur tanah Reduce disturbance Work soil when dry Mulch soil surface Add organic materials (crop residues, compost, manure) Use cover crops diunduh 15/2/2012

48 Wet soilMoist soilDry soil KONSISTENSI TANAH Soil consistency states for a sand and a clay soil (friable soil is best for tillage).

49 Compaction Aggregate destruction Puddling and clods Surface crusts Improving tilth Soil channels SIFAT OLAH TANAH Kemantapan agregat tanah dapat didefinisikan sebagai kemampuan tanah untuk bertahan terhadap gaya-gaya yang akan merusak. Gaya-gaya tersebut dapat berupa kikisan angin, pukulan hujan, daya urai air pengairan, dan beban pengolahan tanah.

50 Bulk density (g/cm 3 ) Water content of soil dry wet maximum density PEMADATAN - LENGAS STANAH

51 PEMADATAN TANAH DAN PERTUMBUHAN TANAMAN Silt loam in Arkansas: decreasing D b by 16% increased cotton yields 13% during a normal year 59% during a dry year Medium textured soils in Washington D b > 1.2 Mg/m 3 ; positively correlated with diseases in peas and beans (h pore space= h water storage capacity)

52 EFEK PEMADATAN TANAH Increasing soil compactiong(increasing bulk density)

53 KERAPATAN PARTIKEL = Particle Density Mass of dry soil per unit volume of solids, this EXCLUDES pore space So if you compact a soil, does particle density change?? No!

54 Comparison of bulk and particle density g/cm 3 = Mg/m g

55 Soil Pans Lapisan tanah yang diperkeras – Claypans – Fragipans – Plinthite – Caliche and duripans Any harden layer is called a pan Claypans occur with extreme illuviation Fragipans are a hard brittle claypan Plinthe is a tropical hardpan that can not be soften by wetting Caliche and duripans, layer of soil cemented by lime cement leaving white hardened layer

56 PORI TANAH - POROSITAS If you compact or till a soil, the pore space decreases. Large pores are filled with air Small pores are filled with water Clay soils have greater total pore space than sandy soils % PS = 100 * (1-[D b /D p ]) Porositas tanah erat hubungannya dengan bulk density serta permeabilitas. Apabila total ruang pori tinggi maka memiliki tekstur tanah yang halus yang dapat menyimpan air dan udara dalam tanah sehingga menyebabkan kerapatan massa (bulk density) yang rendah.

57 % Pore Space = 100 * (1-[D b /D p ]) PORI TANAH - POROSITAS Permeabilitas merupakan kemampuan tanah untuk meneruskan air atau udara. Permeabilitas umumnya diukur sehubungan laju aliran air melalui tanah dalam suatu massa waktu dan dinyatakan sebagai cm per jam. Hal ini mengakibatkan pergerakan udara yang berhubungan dengan volume tanah yang kosong, bukan ukuran pori dan kesinambungan ruang pori.

58 h Clay content A pattern to note: As clay content increases, pore volume increases and bulk density decreases PORI TANAH - POROSITAS

59 PORI MAKRO - MIKRO Macropores are usually air-filled, whereas micropores are typically water- filled The size of pores rather than their combined volume is the important factor in determining soil drainage, aeration, and other processes

60 HUBUNGAN TEKSTUR DENGAN PORI (data for 10 cm depth) TextureO.M. (%) Total pore space (%) Micropores (%) Macropores (%) Sandy loam 242 Silt loam good structure poor structure

61 Color as a guide to soil use – Dark brown to black – White to light gray – Light brown, yellow to red – Bluish-gray – Mottled colors Describing soil color WARNA TANAH …. Diunduh 15/2/2012

62 Hue (e.g., 5R) tells you general shade; DOES NOT tell you how dark the soil is Value (e.g., 5R 5/ ) tells you how dark the soil is: (0 darkest) may indicate current moisture status (dark = wet) and/or amount of organic matter Chroma (e.g., 5R 5/8) tells you color intensity (0 = gray). Indicator of hydrologic regime (well drained =  O 2 = high chroma) “quantified” using the Munsell system WARNA TANAH

63 Hue, Value & Chroma WARNA TANAH

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65 Tanah-tanah coklat tua hingga hitam O.M. can reach high level in waterlogged soil Usually smells sour, oily O.M. can also reach high level in aerated soil. It smells earthy Dark parent materials can affect color of soil..smells chalky Soil colorSoil attributes Environmental conditions Brown to black (surface horizon) accumulation of organic matter (OM), humus low temperature, high annual precipitation amounts, soils high in soil moisture, and/or litter from coniferous trees favor an accumulation of OM

66 Tanah-tanah Putih hingga Kelabu Muda Light color may indicate the presence of chemicals such as gypsum or other salts Munsell soil color chart. diunduh 15/2/2012

67 Tanah-tanah Coklat muda, Kuning, Merah Indicate iron oxides, indicates good drainage Blue-gray soils indicate a lack of oxygen in the soil Mottled wetland soils indicate waterlogged soil for at least part of the year Bright-light Eluvial horizon (E horizon) In environments where precipitation > evapotranspiration there is leaching of sequioxides, carbonates, and silicate clays. The eluviated horizon consists mainly of silica Yellow to reddish Fe 3+ (oxidized iron) Well-aerated soils Soil colorSoil attributesEnvironmental conditions

68 Deskripsi Warna Tanah The Munsell system is a widely used color I.D. system Hue is the color such as red or yellow Value is the lightness or darkness of hue noted by numbers zero to ten Chroma is the purity of the dominate color denoted by a number urhttp://vro.dpi.vic.gov.au/dpi/vro/vrosite.nsf/pages/soilhealth_prac_soil_colo ur diunduh 15/2/2012

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71 SISTEM MUNSELL A 10YR3/6 soil has: The hue 10YR, a yellow red The value of 3 (dark) Chroma of 6 This is described as a dark yellow brown soil This would be recognized internationally

72 WARNA TANAH - DRAINAGE ….. Diunduh 15/2/2012

73 DRAINAGE INTERNAL TANAH. … Diunduh 15/2/2012 Important for proper plant growth Permeability can be determined by the color of the subsoil. Grey with some red or yellow streaks - poorly drained soils Yellowish-brown or reddish brown with some grey mottling - as internal drainage improves Uniform bright color with few or no grey streaks or mottling – good internal drainage and aeration Poorly drained Water is removed so slowly in relation to supply that the soil remains wet for a comparatively large part of the time the soil is not frozen. Excess water is evident in the soil for a large part of the time. Subsurface flow or groundwater flow, or both, in addition to precipitation are the main water sources; there may also be a perched water table, with precipitation exceeding evapotranspiration. Soils have a wide range in available water storage capacity, texture, and depth, and are gleyed subgroups, Gleysols, and Organic soils.


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